1. Field of the Invention
This invention relates to an admixture for hydraulic cement containing, as an effective component, an acrylamide amphoteric polymer produced as a result of Hofmann degradation reaction. More particularly, the present invention relates to a sophisticated admixture for hydraulic cement that prevents deterioration in workability of concrete or mortar with the passage of time and permits improvement of constructability and application properties thereof.
2. Description of the Related Art
Hydraulic cement composition containing cement, water, aggregate and admixtures loses fluidity with the passage of time because cement coheres both chemically and physically when mixed with water. This means that the hydraulic cement composition is deteriorated with the passage of time in constructability and application properties. Such deterioration may sometimes cause troubles in, for example, pumping, the cement composition. If pumping may be suspended for some reason and restarted later, the fluidity of the hydraulic cement composition in a pipe is reduced to cause a rapid increase of the pumping pressure or even clogging of the pipe. The fluidity may be improved with an increased amount of water mixed, which, however, significantly reduces the strength of the resultant concrete.
To overcome the above mentioned problems, various water reducing agents for hydraulic cement have been proposed such as lignin sulfonic acid salt, hydroxy carboxylic acid salt, .beta.-naphthalenesulfonic acid salt-formalin condensation products, sulfonate group-containing melamine-formaldehyde resins, and polycarboxylic acid salt. More recently, it has been proposed to use water reducing agents such as a partial-hydrolysis product of polyacrylamide or a copolymer of an anionic monomer and acrylamide to reduce slump loss (Japanese Patent Publication No. HEI 1-55210/1989). These water reducing agents, however, have only an unsatisfactory level of physical properties including dispersion fluidity, slump holding properties, and storage stability to follow recent development of architecture and civil engineering technologies. With this respect, there have been strong demands for more sophisticated water reducing agents.